It is proposed to study the role of angiotensin II pressor(vascular) sensitivity in control of renin release and blood pressure in hypertensive and other human subjects by using newly recognized properties of saralasin(1-sar-8-ala-angiotensin II). These properties include acting like angiotensin II (agonistic response) on vascular systems with increased pressor sensitivity to angiotensin II(AII) and, ordinarily, acting as a AII antagonist on vascular systems with decreased pressor sensitivity to AII. The studies would include pathophysiological features of the response of the plasma renin activity and blood pressure in these patients to infusions of saralasin and angiotensin II and their relationship to sodium intake, prevailing plasma renin activity and blood pressure. Therapeutic aspects of blood pressure management in selected hypertensives would include a restudying of these pathophysiological responses while on either spironolactone or hydrochlorothiazide and their relationship to blood pressure control (or lack of it). It is anticipated that a better understanding of the role of angiotensin II pressor(vascular) sensitivity in blood pressure control should facilitate the management of hypertension in the future.